Aseptic tanks or sterile tanks are employed within the food industry for temporarily storing a sterile product before it is filled, under aseptic conditions, into some form of aseptic package.
The product may, for example, be milk which has been heated to high temperature during a given predetermined time interval, so that it becomes sterile, so-called UHT treatment (Ultra High Temperature treatment). If the sterile product is packed in aseptic packages, it can thereafter be stored at room temperature for a lengthy period of time.
Aseptic tanks are needed as a buffer between the UHT plant and the filling machines which, for example, are to pack the sterile product into aseptic consumer packages. By employing sterile tanks, excess treatment or processing of the product is avoided when the capacity of the UHT plant does not always correspond to the capacity of the filling machine or machines. The aseptic tank can also be employed for temporary storage in operational disruptions.
Before the aseptic tank is made operational for production, it must, after washing, be presterilized. Today, steam is used to carry this presterilization into effect. Enormous amounts of steam are consumed at a temperature of approx. 130° C. and high pressure. In order reliably to evacuate all air from the tank and the connecting conduits, the steam injection is repeated several times, before the sterilization proper. The steam which is used for the presterilization cannot be recycled, but is ejected straight out into the atmosphere.
The method of presterilization using steam is not totally reliable, since air pockets in a tank and conduit can block the sterilization. Similarly, a certain condensation of steam takes place, above all in long conduits and valves, which lowers the temperature, with poorer sterilization as a result. After the presterilization with steam, both tank and conduits must be cooled down, and this is done using sterile water. A total presterilization with subsequent cooling takes roughly 1 hour and 10 minutes to carry out.